1. Field of the Invention
The present invention relates to a zoom lens system, an imaging device, and a camera. In particular, the present invention relates to: a zoom lens system having, in addition to a high resolution, a small size and still having a view angle of about 80° at a wide-angle limit, which is satisfactorily adaptable for wide-angle image taking, and further having a very high variable magnification ratio of about 30; an imaging device employing this zoom lens system; and a compact camera employing this imaging device.
2. Description of the Background Art
With recent progress in the development of solid-state image sensors such as a CCD (Charge Coupled Device) and a CMOS (Complementary Metal-Oxide Semiconductor) having a high pixel density, digital still cameras and digital video cameras (simply referred to as digital cameras, hereinafter) are rapidly spreading that employ an imaging device including an imaging optical system of high optical performance corresponding to the above-mentioned solid-state image sensors of a high pixel density. Among the digital cameras of high optical performance, in particular, from a convenience point of view, digital cameras are strongly requested that employ a zoom lens system having a very high variable magnification ratio and still being able to cover a wide focal-length range from a wide angle condition to a highly telephoto condition in its own right. On the other hand, in recent years, zoom lens systems are also desired that have a wide angle range where the photographing field is large.
Various kinds of zoom lens system as follows are proposed for the above-mentioned compact digital cameras.
Japanese Laid-Open Patent Publication No. 2009-047903 discloses a zoom lens that, in order from the object side to the image side, comprises five lens units of positive, negative, positive, positive and positive, wherein, at a telephoto limit in comparison with a wide-angle limit, the interval between the first lens unit and the second lens unit increases, the interval between the second lens unit and the third lens unit decreases, the interval between the third lens unit and the fourth lens unit varies, the interval between the fourth lens unit and the fifth lens unit varies, the fifth lens unit is fixed at the time of magnification change, the second lens unit is located on the image side at a telephoto limit, and wherein the focal lengths of the entire system at a wide-angle limit and at a telephoto limit, the focal lengths of the respective lens units, and the amounts of movement of the first and the second lens units satisfy a particular relation.
Japanese Laid-Open Patent Publication No. 2009-042271 discloses a zoom lens that, in order from the object side to the image side, comprises four lens units of positive, negative, positive and positive, wherein the intervals between the individual lens units vary at the time of magnification change, the first lens unit moves with locus of a convex to the image side, and is located on the object side relatively at a telephoto limit than at a wide-angle limit, and wherein the focal length of the entire system at a wide-angle limit and the amount of movement of the first lens unit satisfy a particular relation.
Japanese Laid-Open Patent Publication No. 2008-292733 discloses a zoom lens that, in order from the object side to the image side, comprises four lens units of positive, negative, positive and positive, wherein the respective lens units move at the time of magnification change, the first lens unit is located on the object side relatively at a telephoto limit than at a wide-angle limit, the fourth lens unit moves with locus of a convex to the object side, and wherein the imaging magnifications of the third and the fourth lens units at a wide-angle limit and the imaging magnifications of the third and the fourth lens units at a telephoto limit satisfy a particular relation.
Japanese Laid-Open Patent Publication No. 2007-003554 discloses a zoom lens that, in order from the object side to the image side, comprises four lens units of positive, negative, positive and positive, wherein at least the first and the third lens units move at the time of magnification change, the first lens unit moves to the object side at the time of magnification change from a wide-angle limit to a telephoto limit, and wherein the focal lengths of the entire system at a wide-angle limit and at a telephoto limit, the focal lengths of the first and the third lens units, and the amount of movement of the second lens unit satisfy a particular relation.
Japanese Laid-Open Patent Publication No. 2006-171655 discloses a zoom lens that, in order from the object side to the image side, comprises four lens units of positive, negative, positive and positive, wherein the interval of any lens units is varied to achieve variable magnification, and wherein the focal lengths of the entire system at a wide-angle limit and at a telephoto limit and the focal lengths of the respective lens units satisfy a particular relation.
However, each of the zoom lenses disclosed in the above-mentioned patent documents has a low variable magnification ratio relative to the number of lenses being used, and has a small view angle at a wide-angle limit, and hence does not satisfy the request for digital cameras in recent years.